1. Field of the Invention
The present invention relates to a valve timing adjusting device for an internal combustion engine for adjusting an opening and closing timing of at least one of intake and exhaust valves. Hereinafter the internal combustion engine is referred to as an engine. The opening timing and the closing timing of at least one of the valves are referred to as valve timing.
2. Description of Related Art
A valve timing adjusting device is known that is provided in a transmission system for transferring a driving torque of a crankshaft as an engine drive shaft to a camshaft as a driven shaft, and permits of adjustment of the camshaft functioning to open and close intake or exhaust valves in an engine. This valve timing adjusting device changes a rotational phase of the camshaft relative to the crankshaft to thereby adjust the valve timing for improving the engine output or the fuel economy. The rotational phase of the camshaft is referred to as a phase.
Another valve timing adjusting device is known that changes the phase of a camshaft relative to a crankshaft using an oil pressure. The device, however, has a problem where in controlling a phase change with high accuracy, it demands a certain stable condition need for controlling an oil pressure even when in an environment of low temperature or just after start-up of an engine.
Still another valve timing adjusting device that allows the phase of a camshaft relative to a crankshaft to be changed using not an oil pressure but an electric motor is disclosed in JP-U-4-105906 that is an application publication for the utility model registration. This device is designed such that torque is applied to a rotary shaft by an electric field caused by an electromagnetic unit in an electric motor and then the torque on the rotary shaft is transmitted to a camshaft for inducing a phase change.
The device of the patent literature 1 also has following problems. The whole of the electric motor rotates together with a sprocket which receives the driving torque from the crankshaft, causing an inertia weight on the device to becomes large. This leads to deterioration of the durability of the device. Beside, energizing the electromagnetic unit of the electric motor which is rotating needs a slide-contact connection member such as brush which electrically connects a terminal in the electromagnetic unit and a terminal of wiring with each other by slide contact, the wiring being for the supply of an electric current to the electromagnetic unit. Such a slide-contact connection member is apt to wear, bringing about low durability and radio noise.